Flameless atomic absorption spectrophotometry and neutron activation analysis have been used for quantitation of platinum, magnesium, calcium, copper, zinc, iron, and some other elements in biological tissues and fluids. The analyses are important in biochemical, pharmacokinetic, and binding studies. Very sensitive analytical techniques are necessary because, in most instances, the elements are present in trace concentrations, and in many cases, the sample size is very small as well. Separation techniques including ion-exchange chromatography, solvent extraction, and electrophoresis have been used to purify samples, fractionate and concentrate chemical species before analysis, and eliminate substances interfering with trace-level assays.